Adhesives comprising an aqueous dispersion of polyvinyl acetate,thermosetting cross linking resin and a critical amount of methyl cellulose



United States Patent US. Cl. 260-14 3 Claims ABSTRACT OF THE DISCLOSURE The instant invention relates to non-bubbling, heat curable water-based polyvinyl acetate thermosetting resin adhesives comprising, in addition to the resins noted, water-soluble methyl Cellulose in an amount suflicient to form a non-elastic continuous film on the adhesive surface when exposed to curing temperatures.

BACKGROUND OF THE INVENTION.

I At the present time adhesives are usedin which the resinous components arepolyvinyl acetate and thermosetting resins. While satisfactory for most uses, it has been found that when subjected to elevated temperature as at about 350-500" F., as vin the preparation of oil filters when filter paper is adhered to, other substrates, such adhesives bubble and splatter the filter paper making the adhesive unsuitable for this use. In addition, the

acetate resins in the proportion of about 1 to about 2 parts by weight of medium molecular weight acetate for each part by weight of high molecular weight acetate. The terms medium and high molecular weight are meant to denote a range of molecular weight as understood in vinyl acetate polymerization art. Thus, medium molecular weight is from about 30,000 to about 80,000 and high anything over about 100,000.

The thermosetting resin used can be any curable compound cross-linkable with the polyvinyl acetate. Preferred are phenol-formaldehyde resoles. Also operative are ureaformaldehyde, phenol-formaldehyde novalaks, and the like phenolic-aldehyde and urea-aldehyde resins. Suitable examples are also set forth in Pat. No. 2,902,459.

It is to be pointed out that the polyvinyl acetate and thermosetting resins used and proportions thereof are those commonly used and well-known in the art e.g., the

weight ratio of polyvinyl acetate resin to thermosetting resin being in the range of 1:1 to 1:5 as disclosed in Pat. No. 2,902,459.

The water-soluble methyl cellulose is the critical component of the composition. Attempts to use other water adhesive channels .along the fluted filtered paper stock of the 'filter...sealing. this porous areaand negating its filtering functionaThischanneling and. bubbling by decreasing the amount of adhesiveat the bonding area leaves a weak and non-continuous cured adhesive film betwen" the paper stock and the metal,'such' as steel or tin, plate adhered to the paper in making the enclosed filter. v v

Attempts have been made in the past to overcome this bubbling by speeding up the curing rate of the resins in order to have an extremely rigid surface film at the earliest possible time to prevent bubbling. Such products do not work satisfactorily since the materials used to increase the curing rate give the product a relatively poor stability and short shelf life.

SUMMARY OF THE INVENTION The present invention provides an adhesive composition which is substantially non-bubbling at the elevated temperatures noted and in which the thin continuous surface film first formed upon heating to cure is substantially non-elastic; the film cracks to permit escape of volatiles which would otherwise exert pressure underneath the film and cause bubbling with the illelfects set forth above.

Briefly stated, the present invention compirses an adhesive that is substantially non-bubbling when cured at elevated temperatuers (above 212 F.) comprising a polyvinyl acetate, a thermosetting resin cross-linkable with said polyvinyl acetate resin, and water-soluble methyl cellulose in an amount sufficient to form a non-elastic continuous fihn on the adhesive surface when exposed to curing temperatures.

DETAILED DESCRIPTION As to materials, the polyvinyl acetate used can be any homopolymer or copolymer latex or emulsion commonly used in making adhesives as more particularly described in Pats. No. 2,902,458 and 2,902,459; and for best results a combination of medium and high molecular weight soluble materials have proven unsuccessful. Thus, carboxymethyl cellulose, hydroxyethyl cellulose, polyvinyl alcoho, polyvinyl pyrrolidone, polyethylene oxide, polyacrylates, polyvinyl methyl ether, and polyvinyl methyl ether/maleic anhydride are not suitable.

The methyl cellulose preferred is one having a methoxy] content of from about 26% to about 33%.

The methyl cellulose is unique. It permits a gelling of the wet adhesive when subject to curing temperature thus resulting in a surface film on the adhesive which cracks to let the volatiles escape through fissures. There is no spattering of the dahesive over the fluted filter paper as is the case with the elastic film of the prior art adhesives when ruptured.

The proportion of methyl cellulose used is important. In particular, the methyl cellulose must be present in such proportion that the film first formed when the adhesive is exposed to elevated temperatures for curing will be non-elastic film; i.e., a proportion of 0.1-6 parts by weight of methyl cellulose for 100 parts by weight of poly- .vinyl acetate solids and preferably 0.5-1 part by weight.

The invention will be further described in connection with the following examples which are set forth for the purpose of illustration only and wherein proportions are in parts by weight unless specifically stated to ,the contrary.

EXAMPLE I Two adhesives were prepared having the followin formulations:

Polyvinyl acetate resin emulsion 1 (55% solids) 38. 8 38. 8 Polyvinyl acetate resin emulsion (55% solids) 29. 1 29. 1 Mehtyl cellulose 8 Phenol-formaldehyde resole solids, P/F ratio of 1.13/224) 19. 4 19. 4 Aluminum slheate 2. 9 2. 9 4 4 9. 4 9. 1

Total 0 100. 0

1 Polyeo 1178s. 2 Polyco 188.

3 Combination of Antifoam AF-fifi (silicone emulsion) and Colloid No. 581 (10% Al stearate 1n 3 parts polyoxyethylene and 1 part Cir-13 paralfin).

Both adhesives were separately tested by being placed in a 50 mm. aluminum weighing dish to a depth of inch. A section of pleated filter paper was placed in the adhesive so that the paper was touching the bottom of the dish. The dish was then placed on a hot plate at 375 F. for 15 minutes until the adhesive cured. The dish was then removed from the hot plate and cooled to ambient temperature. The dish was examined for bubbling and channeling during heating and after cooling.

As to adhesive A, during heating numerous bubbles formed and broke splattering adhesive over the pleated filter paper. In addition, the filter paper was seen to absorb the adhesive splattering thereon. After curing and cooling it was noted that areas of the filter paper as high as 1 inch above the surface of the original adhesive level of A inch were covered with a coating of cured adhesive film. Also, many areas of the filter paper above 1 inch were covered with spots of cured adhesive caused by the splattering.

With adhesive B, no bubbling or spattering occurred during heating nor was any channeling noted. After curing and cooling the dish was examined and it was found that, at most, areas of the filter paper inch above the surface of the original adhesive level of 34 inch were covered with a coating of cured adhesive film.

EXAMPLE 2 A series of adhesives of the following formulations were prepared;

The adhesives were each tested as set forth in Example 1 and in each case no bubbling occurred.

EXAMPLE 3 A series of adhesives are made using the identical formulation set forth in Example 2 except that the polyvinyl acetate homopolymers and copolymers disclosed in Pats. No. 2,902,458 and 2,902,459 are each separately and in turn, substitutde in equal proportions by weight for the polyvinyl acetate disclosed in adhesive A therein. In each instance a non-bubbling adhesive is obtained.

While the precise theory is not understood, it is believed that at the elevated temperatures (up to about 550 F.) used the thin layer of adhesive film first formed includes gel areas in the continuous film. These areas are non-elastic in nature and tend to break or fracture rather than expand thus allowing the volatiles such as water vapor and gas to escape. Heretofore, the use of polyvinyl ..acetate-phenolic resins for the same purpose resulted in surface layers, which before they were fully cured, were still thermoplastic in nature and expanded like rubber. It was the rupturing of these rubbery expansions that caused the bubbling and splattering and channeling referred to above.

It will be understood that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purpose of illustration which do not constitute departures from the spirit and scope of the invention.

What is claimed is:

1. A water dispersible adhesive composition that is curable at elevated temperatures without boiling consisting essentially of an aqueous dispersion of polyvinyl acetate resin, a thermosetting resin cross-linkable with polyvinyl acetate resin selected from the group consisting of phenolaldehyde condensation products and amino compound-aldehyde condensation products, and water soluble methyl cellulose in the proportion of about 0.1 to about 6 parts by Weight for parts by weight of polyvinyl acetate solids, the weight ratio of polyvinylacetate resin to thermosetting resin being in the range of 1:1 to 1:5.

2. The adhesive of claim 1, wherein the thermosetting resin is a phenol-formaldehyde resole.

3. The adhesive of claim 2, wherein the methyl cellulose has a methoxyl content of from about 26% to about 33% and is present in the proportion of about 0.5 to 1 part by weight.

References Cited UNITED STATES PATENTS 1,902,257 3/1933 Moss 260l4 1,909,935 5/1933 Dreyfus 26014 2,474,292 6/ 1949 Weidner et al. 260-14 3,444,037 5/ 1969 Armour 117161 OTHER REFERENCES E. WOODBERRY, Assistant Examiner US. Cl. X.R. 

